/Engine/Source/Editor/VREditor/Public/UI/VREditorUISystem.h
Called when the injected proxy tab manager reports a new tab has been launched, signaling an asset editor has been launched, but really it could be any major global tab.
void OnProxyTabLaunched ( [TSharedPtr](API\Runtime\Core\Templates\TSharedPtr)< [SDockTab](API\Runtime\Slate\Widgets\Docking\SDockTab) > NewTab )